The tetracycline operon system, comprising repressor and operator elements, was originally isolated from bacteria. The operon system is tightly controlled by the presence of tetracycline, and self-regulates the level of expression of tetA and tetR genes. The product of tetA removes tetracycline from the cell. The product of tetR is the repressor protein which binds to the operator elements with a Kd of about 10 pM in the absence of tetracycline, thereby blocking expression or tetA and tetR.
This system has been modified to control expression of other polynucleotides of interest, and/or for use in other organisms. Generally, two types of tetracycline inducible systems for controlling the expression of a polynucleotide of interest are used. The first system is “off” unless the ligand is present, and uses an unmodified tetracycline repressor (TetR) or a truncated reverse mutant tetracycline repressor TetOp binding domain fused to a transactivator (rtTA). The second system is “on” in the absence of ligand, and uses a mutated tetracycline repressor (revTetR) which does not bind the operator elements in the absence of ligand, or a truncated tetracycline repressor TetOp binding domain fused to a transactivator (tTA). Typically, most systems use a tetracycline repressor DNA binding domain fragment fused to a transactivator to regulate expression.
There is a need to regulate expression of sequences of interest in plants, compositions and methods to tightly regulate expression in a plant are provided.